How to fold a traditional origami menko 

An elegant and useful envelope folded from a single, square sheet of paper. A word of warning: People often don't realize it opens once then opens twice. I've found it's easier to demonstrate how it works than it is to explain it.
More tips and photos, and an amusing story about when I began using them in my Etsy shop to ship tiny cranes and frogs in. You can read about how I was almost tearing my hair out and paper type suggestions in the menko's blog post over on Patreon: / 35131871